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justins7
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# Posted: 21 Jun 2018 09:37am
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I still have not determined the best way to insulate my cabin on a limited budget. Temps get down to -15 F, so I need to do something.
The photo shows the sleeping loft, about 12 x 16', a bit less than 6' high at the peak. The beams are pretty shallow.
I got a quote from a spray insulation guy to spray it on the ceiling (without finishing, covering or venting it). But then how would it be finished/covered to allow for moisture venting? Does spray foam need venting to the outside?
Would it need a roof ridge vent?
I am tempted to just buy rigid foam and cram it in there with a gap between the roof and the foam, and leaving space at the bottom for it to vent out, but not sure.
Creative low-budget ideas are welcome!
Thanks!
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morock
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# Posted: 21 Jun 2018 02:55pm
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The good about foam is it acts as a vapor barrier, the bad is, if there is a fire the smoke from the foam will kill you quick. Should be covered with a fire resistant material. Personally, that small area could be heated with a good woodstove with no insulation. Even a bad wood stove, but would look for one with a long burn time. Just my two pennies.
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Borrego
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# Posted: 21 Jun 2018 03:20pm
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Since you have such limited headroom, you are stuck with few options.....fill those rafter bays with insulation and drywall/TG over them is probably the most economical. You can install rigid foam on the roof and then reroof over it.....
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justins7
Member
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# Posted: 21 Jun 2018 07:46pm
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It is a very small, though cozy, sleeping loft. We heated it with a good electric space heater, which is fine most of the time, but when it was down to -15 F outside we couldn't get it warmer than 30-40s (that was the extreme).
Borrego, if I fill the bays with insulation and then drywall (or better, tongue and groove) over it: what about venting?
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Princelake
Member
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# Posted: 21 Jun 2018 08:51pm
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Staple up some attic vents then get your spray foam guy to spray it. 3" of spray foam has a R20 rating.
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Borrego
Member
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# Posted: 21 Jun 2018 09:02pm
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Like Princelake says....or put a roof ridge vent in....
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creeky
Member
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# Posted: 22 Jun 2018 08:48am
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If you stuff polyiso sheets in, cut them a bit loose and then spray foam the edges. You'll get a better seal.
Foam on the outside of the roof, as Borrego mentions, is a great idea. I did that. Worked a treat. And it eliminates the thermal bridging off the joists.
Inside like that, I would think about Roxul (mineral wool), not as high a R value, but fireproof and non-toxic. Plus you'll get some sound dampening.
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xtolekbananx
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# Posted: 22 Jun 2018 09:39am
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I have a similar sleeping loft to you, only smaller and same type of roof. What I did is I cut a ridge vent and holes in soffit. I covered holes in soffit with screen so the bugs dont get in. Then I used rigid insulation with 1 inch gap between the insulation and roof sheeting. I cut the insulation so it fits between the rafters and sealed the gaps. Had it like this for over a year and no moisture problems.
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Wilbour
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# Posted: 22 Jun 2018 10:07am - Edited by: Wilbour
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My 10 x 16 has a 12:12 pitch so I put in collar ties about a foot down from the peak. Then I used 1" rigid foam and secured it to the underside of the rafters and taped the seams. This created a large air pocket between each rafter up to the triangle pocket at the peak. I put in two vents in that area and screened in the lower opening of the space between each rafter.
This doesn't provide a lot of insulation but my loft is closed off of the cabin area when trying to heat up the living space.
My shingles are kept cooler because of the natural airflow under the roof .
There has been much discussion on a vented or hot roof.
I have a had a lot of success with my setup. I like a cooler loft in the fall as it makes for better sleeping.
In the summer I open the hatch and the windows in the loft to create an upward draft which brings in fresh air downstairs
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Wilbour
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# Posted: 22 Jun 2018 10:35am - Edited by: Wilbour
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I was going to do what xtolekbananx & creeky said but didn't want to take the time. Now I wonder what was more work since I was left with shiny foil for a wall/ceiling. When I installed paneling over this I had a hard time finding the rafters to nail into and keep the nail straight as it had to go through the foam before hitting the wood.
More effort before would have been less after.
I had seen an interesting documentary on surviving the arctic weather with traditional ways and how the Inuit would build a sleeping tent within a larger tent. The results were amazing. Thin animal skins as a barrier kept the researcher so warm in his inner tent that he slept without any coverings. The science behind this was that the heat had to escape from the small tent and then progressively escape the larger tent. The pocket of air in the larger tent was acting as insulation.
This is , in theory, is what I try to do with my closed off loft in the winter.
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creeky
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# Posted: 22 Jun 2018 12:37pm
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Quoting: Wilbour This is , in theory, is what I try to do with my closed off loft in the winter.
what's that? pitch a tent?
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Wilbour
Member
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# Posted: 22 Jun 2018 02:23pm
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No silly.
Have a main heated area and a secondary unheated area above. The second area is insulated though.
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rockies
Member
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# Posted: 22 Jun 2018 07:43pm
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The problem isn't really how to insulate the roof, the problem will be what happens to any moisture trapped inside the ceiling cavity. Not only is there moisture from cooking, indoor plumbing and also from the human body but there can be a tremendous amount of moisture driven into the roof structure from outside.
Most people think that if they stuff the rafter bay full of insulation they've created a sound roof, but then there's the venting, the air baffles, vapor barriers etc to deal with. Coupled with that a lot of people have very small roof rafters, so for a 2x8 rafter, once you subtract the air gap (about 2 inches) you only have about 5 1/2" of insulation, which isn't great.
The best method is to spray foam the underside of the roof sheathing. This product creates an insulation layer as well as a vapor barrier all in one so you don't need to vent or have an air gap. The interior rafter bays must be covered as a fire safety measure though.
Why not try a DIY product like Tiger Foam? They will ship you out a kit sized for your project and when it's used up they take back the tanks for you.
https://tigerfoam.com/sprayfoaminsulation/order-products/spray-foam-insulation-bulk-s pecials/
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justins7
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# Posted: 24 Jun 2018 05:24pm
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Thanks for the replies.
Rockies, I did get a quote to have spray foam done, which wasn't too expensive. But he never explained about the venting situation.
So, with spray foam, is there no moisture that forms? Or does the moisture form on the exposed side of the dried foam?
Thanks!
Justin
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rockies
Member
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# Posted: 24 Jun 2018 06:29pm - Edited by: rockies
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Moisture is always in the air. The reason spray foaming the underside of the roof sheathing is such a good method of insulating is because the foam causes the interior surface of the wood to stay much warmer so that the moisture in the air won't condense on the sheathing (especially in the winter) and start mold growing.
The benefit of not having to vent is a bonus. Since you will have to add an interior finished ceiling (probably t&g boards would be easiest) don't add a poly vapor barrier behind the finish ceiling. The plastic would only trap whatever moisture does get in and lead to rot.
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ILFE
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# Posted: 24 Jun 2018 07:20pm
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No advice on insulation for those temperatures, as I live in Southeast Asia. I have to open my freezer to experience anything near that cold here.
However, I did want to say, I love gambrel roofs. Had I ever built a cabin while living in the US, it, most definitely, would've had a gambrel roof and loft.
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justins7
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# Posted: 25 Jun 2018 11:23am
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So, with closed-cell spray foam, you don't need to vent? You only need to have the exposed foam covered (t + g boards), correct?
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snobdds
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# Posted: 25 Jun 2018 01:25pm
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Yes, no venting required with closed cell spray foam. It's really the best solution for cabins that only see seasonal usage.
Closed cell spray foam has the following qualities...
Thermal Break
Insulation
Vapor barrier
Increases shear strength in framing, glues everything together.
No venting required.
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NorthRick
Member
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# Posted: 25 Jun 2018 03:51pm
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Quoting: justins7 So, with closed-cell spray foam, you don't need to vent? You only need to have the exposed foam covered (t + g boards), correct?
Correct. BUT, it has to be applied correctly and thoroughly so moisture can't get behind it.
A big potential downside is that if you develop a leak in your roof you could have a lot of rot occur before you discover it.
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